It has become common practice in the automotive industry to position an acoustic barrier adjacent a steel body panel separating the engine compartment of a vehicle from a passenger compartment to reduce the level of noise entering the passenger compartment from the engine compartment. Typical vehicle acoustic barriers comprise a noise-insulating panel made of self-supporting, thermoset materials such as reaction injection molded polyurethanes, and thermoplastic materials, such as highly filled ethylene vinyl acetate copolymer, polyvinyl chloride and polypropylene, which is usually positioned on the passenger compartment side of the steel wall separating the engine compartment from the passenger compartment. The noise insulating panel is typically spaced from the steel wall, and the space between the noise insulating panel and the steel wall may be filled with loosely structured materials, such as foams, fibers, flakes or the like, to improve high frequency absorption of noise. In some cases, a fibrous mat or foam panel is fixed to the thermoplastic noise insulating panel to provide a sound insulating system that can be installed as a unitary assembly.
Known automotive acoustic barriers are comprised of substantially continuous sheets or panels having openings only where absolutely necessary to allow passage of the steering column and other vehicle controls and systems that must pass from the engine compartment to the passenger compartment. These various component pass-through areas provide more significant sources of noise than areas of unbroken steel wall and noise insulating panel.
A known alternative acoustic treatment is to use absorbing material placed against the steel wall, although this construction will allow for absorption in the passenger compartment, the overall noise level without the barrier layer is usually higher.
In order to achieve improved vehicle fuel economy, it is desirable to achieve excellent noise insulating properties with a lighter weight acoustic barrier which can be easily installed on the engine compartment side or on the passenger compartment side of a steel wall separating the engine compartment from the passenger compartment.